<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <meta http-equiv="X-UA-Compatible" content="ie=edge">
    <title>Document</title>
    <style>
        body{
            background-color:  red;
            /* 设定默认css样式背景颜色为红色 */
        }
        @media screen and (max-width: 768px){
            body{
                background-color: green;
            }  
        }
        @media screen and (min-width: 768px) and (max-width: 992px){
            body{
                background-color: blue;
            }
        }
    </style>
</head>
<body>

</body>
</html>